The present invention pertains to improvements in fluorescent gas analyzers.
Fluorescent gas analyzers essentially include a reaction cell having inlet and outlet ports for enabling a carrier gas to flow through the cell; an excitation energy source coupled to the reaction cell for radiating the interior of the cell with excitation energy that causes a given gas to fluoresce in a given wavelength; and a detector coupled to the reaction cell for detecting fluorescence in the given wavelength and for providing a signal that is proportional to the intensity of the detected fluorescence. This signal is integrated over a predetermined interval to provide an output signal that is approximately proportional to the concentration of the given gas within the carrier gas cell. 11 Florescent gas analyzers are useful in measuring the concentration of pollutant gases, such as sulfur dioxide (SO.sub.2) and nitrogen dioxide (NO.sub.2) within various carrier exhaust gases.
Fluorescent detection of SO.sub.2 excited by ultraviolet (UV) radiation is discussed in a paper by OKabe et al, entitled "Ambient Sulfur Dioxide Detector Based on a Fluorescent Method", presented at the 65th Meeting of the Air Pollution Control Association at Miami Beach, Fla., June 18-22, 1972, and in Schwarz and OKabe, "Fluorescence Detection of of Sulfur Dioxide in Air at the Parts per Billion Level", Analytical Chemistry, Vol. 46, pp 1024-1028, July 1974. Examples of fluorescent gas analyzers are described in U.S. Pat. Nos. 3,826,920 to Woodroffe et al and 3,845,309 to Helm et al.
The accuracy of prior art fluorescent gas analyzers is impaired by two significant factors. The intensity of the fluorescence and the resultant output signal are dependent upon the intensity of the excitation energy, whereby variations in the excitation energy affect the output signal level. In addition, the fluorescence detector also detects scattered excitation energy, whereby the resultant output signal is proportional to the intensity of the detected fluorescence and the intensity of the detected scattered excitation energy radiated from the excitation energy source.